As one mass spectrometric technique for qualitative and quantitative determination of a target compound contained in a sample, there is a technique called the “MS/MS analysis (tandem analysis)”. For example, the MS/MS analysis is performed using a mass spectrometer having a front mass separator for selecting a precursor ion, a collision cell for fragmenting the precursor ion into product ions, and a rear mass separator for selecting a product ion. One example of such a mass spectrometer is a tandem quadrupole mass spectrometer.
An MRM measurement is one mode of the measurement in the MS/MS analysis. In the MRM measurement, the mass-to-charge ratio of the ions which are allowed to pass through is fixed in each of the front and rear mass spectrometers so as to measure the intensity (amount) of a specific kind of product ion corresponding to a specific kind of precursor ion. Such a combination of the precursor ion and product ion is called the “MRM transition”. In the MRM measurement, ion intensity signals can be obtained with high signal-to-noise ratios, since the two-stage mass separators remove ions which originate from compounds which are not the measurement target or from foreign components, as well as neutral particles. Accordingly, the MRM measurement is particularly effective in such analyses as a quantitative determination of a trace amount of a component.
In order to perform an MRM measurement for a target compound, it is necessary to previously determine the MRM measurement condition. The MRM measurement condition includes the MRM transition as well as the value of the collision energy (CE) for inducing the fragmentation of the precursor ion within the collision cell. Since the magnitude of the CE value affects the generation efficiency of the product ions, a combination of the MRM transition and CE value which yields the highest level of detection sensitivity should be set as the MRM measurement condition.
The MRM transition and CE value have conventionally been determined as follows:
Initially, an analysis operator enters one or more precursor-ion candidates to be generated from the target compound and a plurality of CE-value candidates on a control software program for the mass spectrometer. The control software program determines all possible combinations of the entered precursor-ion candidates and CE-value candidates as the measurement conditions. Subsequently, a product-ion scan measurement is performed using one of those measurement conditions. This task is performed under each of all of the measurement conditions, to acquire product-ion spectra (FIG. 4A). From all of the product-ion spectra obtained in this manner (FIG. 4B), product ions are selected in descending order of the detection intensity, and the combination of each selected product ion and corresponding precursor-ion candidate (MRM transition), as well as the CE-value candidate at which the product-ion spectrum concerned was obtained, are determined as the MRM measurement condition (FIG. 4C; for example, see Patent Literature 1 or 2).
Such a product-ion scan measurement is normally performed under the condition that a standard sample which is the target compound in pure form is directly introduced into the mass spectrometer.